Early anaesthetic (5)

I think it could be either:

Which length description are you looking for?:

ether

(Other definitions for ether that I've seen before include "Rare atmosphere" , "Formerly an anaesthetic" , "Anaesthetic is, strangely, there" , "Volatile organic liquid once used as a general anaesthetic" , "Imaginary interstellar medium" .)

I've seen this clue in The Sun, The Guardian and the Canadiana.

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